Both virDomainInfo and virVcpuInfo have a nanosecond cpuTime field. How
do the two related to one another?

With some experiementing, it appears the virDomainInfo::cpuTime is equal
to the host CPU time used by the qemu-kvm process for the domain. It
also appears that the sum(virVcpuInfo::cpuTime) for a domain is not
equal to the virDomainInfo::cpuTime. Is the virVcpuInfo::cpuTime how
much host CPU time was spent simulating the vCPU? Making the difference
between the sum and the virDomainInfo::cpuTime the overhead of qemu-kvm?